Universal Constant
by AnotherSpoonyBard
Summary: A universal constant is a physical quantity fixed across context and time. Some things are reliably unchanging, despite the way circumstances and conditions fluctuate. Yumichika and Ikkaku have learned over many years that they can rely on each other—come hell or high water. With upheaval in Soul Society, the Gotei 13, and the division they call home, they're going to need to.
1. Chapter One: Yin

Disclaimer: BLEACH belongs to Kubo, Viz, and probably some other people who aren't me.

* * *

 _Universal Constant_

A Bleach Fanfic

 _Chaos Theory_ AU

Chapter One: Yin

* * *

If fear was plucky, and globes were square,  
And dirt was cleanly and tears were glee  
Things would seem fair,—  
Yet they'd all despair,  
For if here was there  
We wouldn't be we.

-e.e. cummings

* * *

 _One month after the Battle of Fake Karakura Town_

The bustle and hum of the Fourth registered only lowly from Isane's room; this was something of a welcome relief to Yumichika, though he'd never admit it.

In keeping with her personality, the space was painted in soft blue, the tatami neat and the floor cushions in front of the table patterned with dainty flowers embroidered into the pastel silk. The walls bore both ink paintings and slightly-less-traditional watercolors, each square with its selected spot, and the fat hibiscus blooms in the vase on the window perfumed the entire space only faintly.

Isane herself sat across the table from him, not bothering to round her shoulders forward to look shorter. Or perhaps only forgetting to. Her cup of tea sat far enough away not to interfere with her work, steam still curling from the delicate ceramic she'd promptly ignored as soon as she'd poured it. She was frowning at the canary-yellow feather held carefully in her left hand, the small scissors in her right ajar but motionless.

Of course, Yumichika appreciated the care she was showing the task, even if he thought she'd do just as well not to worry so much.

"Cut too large first, then trim," he suggested, already following his own advice.

She hummed, brows furrowing a bit, then nodded. "Sorry. It just seems like I should be really careful, considering where they're going." She glanced up, sheepish.

Yumichika couldn't quite get over how different she was—in person, so to speak—from how she was as fukutaichō of the Fourth. All that confidence and certainty just seemed to melt right off her. It was quite the interesting change, though frankly he found it unnecessary and often told her so.

"I promise I won't let them anywhere near my eyelashes if they aren't to my liking," he replied archly.

This, for whatever strange reason, seemed to be the kind of thing that reassured her, and she went back to work with a little more gusto this time.

It wasn't more than another few minutes before the rasp of her blades paused again, though. "Any particular reason you're changing these, by the way? I thought you really liked the ones you have."

Yumichika shrugged, more offhandedly than he really felt. "I do. That doesn't mean I want to keep them forever."

Isane made a small noise in the back of her throat, like she didn't quite agree. She was much more sentimental than he was—most likely she read more into the statement than he'd really meant to convey with it.

"I guess… I just figured that now would be the sort of time to hold onto the things that haven't changed. Er—not that this is a big deal or anything." She waved the hand with the feathers in what was probably meant to be a conciliatory gesture. A few pieces fell away from where she'd been trimming, fluffing out into the air and drifting down onto the tabletop like snow. She made a face and cleared her throat, trying to gather them back together.

Yumichika suppressed a laugh by pursing his lips tightly together for a moment. "You're not wrong, I suppose," he said, making a few more delicate cuts of his own. "But I tend to save all that effort for the important things."

He'd never been one to hold onto things clearly on their way out the door, so to speak. And the old Gotei 13, his old place in it—that was already gone, like it or not. He was far too much a realist to pretend otherwise. The best thing to do now was adapt in the way the new reality demanded. Someone had to, and frankly the entire rest of his division was _terrible_ at that sort of thing.

Isane seemed to follow even the unspoken parts of his train of thought. She was quite good at that, he'd discovered.

"How's Ikkaku-san holding up? And the rest of the division?"

Yumichika grimaced for just a moment before smoothing away the ugliness of the expression. "Not well, in either case," he said, expelling a sigh from his nose. "I doubt this will surprise you, but the Eleventh does not do particularly well at self-direction. Nor at processing emotions." The death of their captain and the ongoing absence of their vice-captain had hit everyone hard. As it would, when they'd all built Zaraki-taichō up in their minds as the invincible fighter who could not fall. The goal to be striven towards, and the only person worth serving under in the meantime.

Yumichika did not believe in idols, but even he'd admired the captain a great deal. Mostly for the purity and simplicity of the way he lived. It had been a particularly beautiful sort of minimalism of purpose. Almost ascetic, though he doubted anyone on either side of the comparison would welcome it.

"Yachiru's… not well, either," Isane replied, her lips pursing. "Unohana-taichō is looking after her as much as she'll allow, but she spends most of her time alone these days. It's hard to know what to say to her."

He nodded. That tracked with his observations, when he'd gone to visit her. Somehow, he doubted the fukutaichō would be returning to the Eleventh. Her life had been symbiotic on Zaraki-taichō's; though there were other people who she liked and would probably eventually draw comfort from, he doubted she'd wish to resume those duties. Besides, vice-captains were appointed by captains, and they still didn't know what would be happening in that regard.

Though they were far from the only division with the problem, they certainly had a unique version of it. No one that Kyōraku-sōtaichō could put in the position would ever really be accepted, because that person would not have felled the previous captain in a fair fight. That would make matters… exceedingly difficult. Yumichika was trying to hold things together organizationally in the meantime, but it was proving quite difficult when the rest of the officers were just non-functional. Perhaps it was time he lit a fire under some of them and tried to at least work through the positively _disgusting_ backlog of paperwork.

"And yourself, Isane-san? The Fourth seems to still be in working order, for the most part." Yumichika resumed his cutting, slowly accumulating a pile of tiny pieces of feather.

"Well, there's been a lot of work, as I'm sure you can guess." Isane shifted in her seat, finally setting the scissors down to take a sip of her tea. "We've honestly only just been able to release the worst-injured of our patients. Poor Ishida-san was in awful shape. And, well, healing Ukitake-taichō is always complicated."

It wasn't the first hint Yumichika had ever come across to this effect, but he didn't press her for more information. It didn't really concern him, and was no doubt sensitive information besides. Isane took her divisional duties every bit as seriously as Yumichika took his, even if what those duties boiled down to was wildly different.

Glancing between his pile and Isane's smaller one, Yumichika set down his scissors as well. "I think there's enough here. You said there was some kind of living world invention that would make this feasible?"

Isane visibly brightened. "Yes! It's called eyelash glue, I think. Rangiku-san found it in the real Karakura Town. I can use a kaidō to set it faster and make it hold better, but it should help with the application, anyway." She picked up something from the floor next to her and rolled it over the surface of the table towards him.

Yumichika caught it deftly, raising a finely-arched eyebrow at the label. "The living world is quite the place," he said. He was almost envious.

Isane huffed, rising from her seat only to settle herself back down next to him. "Maybe hold off on saying that until we know if this works," she pointed out, adding her collection of feathers to his. "You want both lash-lines, right? Upper and lower?"

"Mhm."

Isane had the steadiest hands of anyone he knew, and Yumichika could swear that her eyesight was flawless. The result of this combination was a precision that probably helped her a great deal in her profession, and also meant she was the only person he'd trust to do this kind of delicate task right next to his eyes. She wore an intent look of concentration as she worked, the occasional glow in his peripheral vision indicating the use of the promised kaidō.

When she was finished, she handed him a small mirror. Yumichika blinked a few times to make sure everything was holding, then raised it to eye level.

Yellow had been an excellent color selection. Isane's work, as ever, was quite impressive; she'd concentrated the feathers at the outer corners of both eyes, and blended them seamlessly with his actual eyelashes.

"You, my dear Isane-san, are wasted on healing people."

She snorted, an unladylike sound if ever there was one, and rolled her eyes at him. "My true calling being…?"

Yumichika smiled slyly at her. "Art."

* * *

He was entirely unsurprised when he made it back to the division that night only to find Ikkaku drinking alone. Well, _alone_ in that he was the only one still awake, at least.

At any other time and for any other reason, Yumichika might have rolled his eyes at this discovery, but he was inclined to let this one pass. Few people would understand the real nature of Ikkaku's grief, but he was one of those few.

So instead, he stepped neatly over a few unconscious lower seats and settled himself to the other man's left. Plucking one of many bottles of sake off the ground, Yumichika took hold of the untouched dish next to Ikkaku's knee and poured himself some as well.

Whenever anyone but him chose the sake, it was terrible, but he knocked the first one back in a single gulp anyway, his mouth forming a disapproving moue at the sharp taste of it. Oh well.

"Is it weird that I'm gonna miss her callin' me pachinko-head? Fuckin' brat."

Yumichika arched both brows. "She's not dead, you know."

Ikkaku's mouth pulled to the side. Obviously, he knew that, but he was wallowing so deeply right now that Yumichika wouldn't be surprised to get an earful of melodrama at any moment.

"Yeah, but she ain't ever gonna be the same. None of us are."

Hm. Not as bad as he'd been expecting. Yet.

Yumichika poured himself another drink, intentionally setting the bottle on his opposite side, where Ikkaku could neither see nor easily reach it. "That doesn't mean she'll never insult you again."

"Dammit, Yumichika, that ain't what I mean, and you know it." Ikkaku made a noise that might have almost been a snarl had he put any real aggression into it. It was disappointing, in a sense.

"I know. But you're not very good at _saying_ what you mean." Yumichika sipped more slowly from the second cup, the pleasant hum of Isane's room and conversation already ebbing from his mood. How annoying.

A month wasn't enough time to grieve. Yumichika knew that. But really, it should be enough time to start thinking about the other things that had to be done in life. Ikkaku could not keep refusing to acknowledge the real issues in front of them, even if they were difficult to cope with. Even if they meant that the both of them would have to take a good, long look at themselves and decide where to go from here. Who to become. Yumichika knew who he wanted to be—but Ikkaku was always slower about things like this.

"I mean I dunno what the fuck we're gonna do now," he said at last, setting his empty cup down too hard on the engawa's wooden floor. It wasn't like it hadn't been scuffed thousands of times already. "Nothing's the same anymore!"

Yumichika licked a drop of sake from the lip of his dish, staring out at the practice yard. The best seats in the Eleventh didn't face anything as mundane as a garden or the edge of a forest. This was where the officers watched fights. He could see Ikkaku in the periphery of his vision, narrow eyes locked on the motion. Waiting for a response, certainly.

"We're the same." Yumichika gave in and cut a glance towards Ikkaku, lifting both shoulders.

No doubt as individuals they would change a great deal from here on out. And perhaps some of the unimportant details would shift around between them, too. But the core of what they were, as a unit, was by far the most constant thing in either of their lives. It had been the same since before Kenpachi Zaraki, since before the Gotei 13 and the Eleventh Division, and it would be the same after. Long after.

Ikkaku raised a hand to the back of his neck, rubbing his nape like he had an itch. "Yeah. I know."

"Well that's the place to start, then. Whatever you're doing, I'm doing. And whatever I'm doing, you are. Is there anything you particularly want to be doing right now?"

Yumichika knew Ikkaku liked being here. Truthfully, he did too. More than he'd liked being out in the Rukongai. But if Ikkaku decided that the thing to do was leave the Seireitei, temporarily or permanently, he wouldn't even have to debate what _he'd_ do. Both of them led, both of them followed, and it usually just worked out that whoever felt the greater need to go one way instead of another picked the direction.

Ikkaku shook his head. "I dunno. Fuck. I thought I was gonna die under his command, you know? And fight till then, and just… _fuck_." Ikkaku's fist hit the floor, breaking clean through one of the boards and sending the sake dish skittering sideways. Still none of the sleeping shinigami woke.

Expelling a breath, Yumichika shifted out of seiza and crossed his legs under him instead. They both sat just outside the half-circle of warm light cast by the lantern in the window. It threw Ikkaku's face into shadow, softening the foxlike angles of his features. There wasn't much that could really be said about that—what Ikkaku said was true. Yumichika had known it was true. And the goal was now impossible. The posts removed, so to speak.

"This is what's left of him," he said slowly, gesturing over at the unconscious officers and then out towards the barracks more generally. "Why not die serving all of this instead?"

It was hardly the same. The division writ large didn't have the same magnetism, the same strong sense of purpose. The same minimalistic appeal. They weren't especially unified by anything except a penchant for violence and an admiration for a dead man who'd lived a life soaked in it. Zaraki-taichō had been a lot of things, but he wasn't a leader, exactly. He just got followed. Yumichika could make the distinction relatively easily, but he didn't think that it was obvious to everyone.

Ikkaku seemed unsatisfied. "This your way of saying I should tell 'em about my bankai? Be the captain?" The light struck his eyes sideways, giving them a dangerous glimmer.

It didn't faze Yumichika. "Not if you don't want to. But for what it's worth, I doubt your secret is all that secret. It's unlikely anyone will try to make you a captain unless you decide you want to be one." Quite possibly not even then. Ikkaku wasn't really a leader either. At least not yet. Maybe if he decided he wanted to be one, he could, but right now the best he'd be able to do was _get followed_. With less enthusiasm than his predecessor.

The statement surprised him, from the way his mouth dropped halfway open. Like he wanted to say something but didn't know what. "I never told anyone but you an' Renji about that. You saying he spilled?"

"No, Ikkaku. I'm saying that the Seireitei has an entire division whose _job_ is gathering intelligence and reporting it to people with authority. And you're not subtle."

Keeping a secret like that from the Eleventh was easy. He knew this from experience. Keeping it from the Second was likely impossible.

In the long silence that followed, Yumichika polished off his sake, allowing Ikkaku the opportunity to collect his thoughts.

"I still dunno about this. We've only ever decided this shit one way in the Eleventh. And that's the way it should stay."

The sake dish clinked gently on the ground. "So you want to find out exactly what happened, then?"

What they'd been told was that Zaraki-taichō had fallen in battle against an Arrancar, and that the Arrancar in question had in turn been killed by one of the other captains. Perhaps it would satisfy Ikkaku if the captain in question was willing to entertain a challenge. Or just accept two transfer officers. That would depend on him.

"Yeah. Yeah, I gotta know how it went. You know how we can do that?"

"As a matter of fact, I do. But you aren't going to enjoy it."

* * *

The Twelfth wasn't, in general, a place that anyone else visited unless they had to. _Really_ had to. Experimental medical procedures like limb and organ replacement were about the only things that could drag anyone with a sense of self-preservation anywhere near Mayuri Kurotsuchi. Yumichika was sure they had to talk about the place in extremely neutral terms at the Academy, or it would never see one willing recruit.

Naturally, Ikkaku was just as displeased to be here as Yumichika had predicted. Only two things universally unnerved members of the Eleventh: the Twelfth in general, and Retsu Unohana in particular.

Fortunately, they need not venture too far into the place; Yumichika had asked Isane to put him in touch with Nemu Kurotsuchi for this, and she was waiting for them near the gate when they arrived.

She certainly had a demure appearance, though he had to wonder how useful the skirted version of the uniform really was. The aesthetic value of the choice was obvious, but became less so when considering the potential wounds it made her that much more vulnerable to. Even for shinigami, scars were forever.

Kurotsuchi-fukutaichō bowed, hands folded neatly in front of her. "Welcome," she said, voice soft, and dull to the point of nearly being toneless. "Isane-san indicated that you wished to access some of the battle footage in our archives?"

Ikkaku was still busy suspiciously scanning the grounds, so Yumichika nodded. "Yes, thank you. We're looking for anything recorded from Zaraki-taichō's time in Hueco Mundo."

She blinked, then dipped her chin. The gesture was delayed, like she'd almost forgotten to do it. "Please follow me. Mayuri-sama does not like it when his work is disturbed, so it is best if you do not linger or touch anything on the way."

"You don't gotta worry about that," Ikkaku grumbled, falling in behind Yumichika and Kurotsuchi.

It seemed that their so-called archive was an outbuilding, which minimized the number of other shinigami they ran into. The few that seemed to be about mostly kept their eyes down, hurrying to and fro with what must have been either chores to do or deliveries to make. None of them looked much like officers—but then all the seated members probably spent most of their time in the labs. Probably underground, since at surface level the only things Yumichika could see were barracks, a mess hall, and some exceedingly ordinary-looking offices. The training yard had overgrown, grass poking out from the brown dirt in a way it never would have had time to at the Eleventh. Or probably anywhere else.

Kurotsuchi slid open the door to the outbuilding, leaving it open for the two of them to follow. Stepping inside, they were swallowed by darkness, at least until she lit a small kidō light over their heads. Various boxes and a few crates were placed against the walls of the single room; of more interest was the staircase. It proved to be narrow, forcing them to continue in single-file on the way down.

It didn't look like any archive Yumichika had ever seen. There was no more than one shelf of books; the rest of them seemed to be stacked with data discs and chips, organized in some way he couldn't really make sense of at first glance. One whole wall was taken up by a massive screen, a large command console stretched out in front of it.

From the way Kurotsuchi moved immediately to one of the shelves, he supposed she must know where the information they were looking for was kept. He squinted as she moved several disc cases to the side, labeled with what looked to be names and rough time stamps. The one she picked out of the stack said 'ZARAKI v. SEXTA ESPADA, HUECO MUNDO INVASION.'

"Cameras were deployed with the authorized invasion force," Kurotsuchi explained, removing the disc from its case and crossing to the command console. "Ordinarily, we would not have had data from the time before those individuals entered Hueco Mundo. However, Aizen's fortress had nearly universal surveillance measures as well, and Mayuri-sama salvaged parts of the data before returning to Soul Society. We've spent much of the last month sorting through it, and prioritizing certain items for the Sōtaichō."

"Pretty empty down here right now," Ikkaku observed.

"Yes," she replied. "The work was mostly completed last week. Mayuri-sama was impatient to return to his personal projects, for which he requires assistance." With a few keystrokes and what looked like a retinal scan, Kurotsuchi activated the screen. It flickered in the dark, before resolving into a still image: Zaraki-taichō grinning widely at what had to be an Arrancar, his hair a bright shade of blue and a mask fragment attached to his face near the jaw.

"This the one?" Crossing his arms over his chest, Ikkaku narrowed his eyes at the screen.

Kurotsuchi's lips thinned. "Not precisely. This is the Sexta Espada, Grimmjow Jaegerjaquez. He had a match with Zaraki-taichō prior to his death. If you wish, I can advance the footage to the end." Glancing back over her shoulder, she moved her eyes between them.

Ikkaku shook his head immediately. "No. If this is his last fight… I wanna see the whole thing."

"As you wish." Tapping a button on the console, Kurotsuchi stepped back, moving to stand back near the stairs.

Yumichika fixed his eyes on the screen as it began to move. The Arrancar, carrying Yuzu Kurosaki on his back of all things, stopped a decent distance from the captain, setting her down.

"Grimmjow. We finally gonna finish this?" Zaraki-taichō's tone was one Yumichika knew well. It had the bite of anticipation in it. Whoever this Arrancar was, they'd met before, and the captain had been looking forward to the fight.

"You got that right. But first—Yuzu." The same tone inflected the Arrancar's words, softening only slightly and only on the girl's name.

The little Kurosaki got to work on Zaraki-taichō's wounds. They didn't look like anything serious, but the fact that he let her heal them anyway suggested he was interested in starting on even footing with Grimmjow.

Yumichika glanced once at Ikkaku, but his eyes were still riveted to the screen, face set in a resting scowl. Then the battle began, and he found that _he_ couldn't look at anything else, either.

It was intense from the start: Zaraki-taichō discarded his eyepatch within minutes. Right about the same time they seemed to come to mutual agreement that the warm-up phase of the fight was over. When the Arrancar released his zanpakutō, his form changed. Something like a cat, which made perfect sense considering the name. _Pantera_. He fought with no kidō, just his body, release techniques, and whatever the Arrancar version of _shunpō_ was called.

Zaraki-taichō looked to be enjoying himself more than Yumichika had ever seen him do. A jagged grin stretched wide over his face—unwavering even as both opponents sustained injury after injury. While the captain remained largely immobile, Grimmjow was so fast that even Yumichika had difficulty tracking his motions; whenever he was still enough, it became clear that he wore a mirror-version of that bloodthirsty smile.

If this was how the captain had died, then he'd died in exactly the way he'd always wanted to.

Ikkaku shifted beside him, moving one hand to Hōzukimaru's hilt and resting it there. Even Yumichika's blood was up a bit by proxy, just watching this happen. He felt all his muscles lock into place when they turned to face each other after on particularly brutal pass. Even before they spoke, it was obvious that this would be the last exchange. As of yet, Yumichika had seen nothing that would cause Kurotsuchi to qualify her answer to Ikkaku's question—so what was it?

He must have stopped breathing when the final blows landed, because only after the last of the dust had settled onscreen did Yumichika notice his lungs beginning to burn and inhale again. Zaraki-taichō fell first, rolling over onto his back. A moment later, Grimmjow collapsed too, the victor by seconds, since neither of them seemed capable of again reaching their feet.

"We should do this again somet—"

The captain's words were quickly cut off by a shout.

" _Bakudō #39: Enkōsen_!" Kurosaki threw her hands out, the camera changing angles in enough time for the audience to see exactly what she was trying to do.

But the scythe arcing towards their captain would not be stopped. It slammed into the kidō shield and shattered it, piercing Zaraki-taichō's arm beneath it too before burying itself in his chest. The weapon withdrew, wielded by the hand of a tall, thin Arrancar with a narrow face that reminded Yumichika of some sort of insect. A grasshopper, maybe.

"That _bastard_!" Ikkaku had not taken the interference well; a rattling noise gave away the angry tremble in his hand. Hōzukimaru was knocking against his sheath.

"… is dead, right Kurotsuchi-fukutaichō?" Yumichika finished, looking to her for confirmation. The recording had stopped as soon as the captain vanished.

"Yes," she replied simply, moving back in front of them without any fear of the quaking Ikkaku. She removed the disc from its place in the console and replaced it in the casing she'd drawn it from. "We do not have footage of that, however."

"Who killed him, then?" Ikkaku snarled.

For a moment, the corners of Kurotsuchi's eyes pinched, like she'd nearly flinched but stopped herself before it happened. "Reports indicate that Unohana-taichō did. However, the only person who could confirm or deny this with certainty is Unohana-taichō herself."

"How come?" Yumichika asked, lifting a brow. "You said cameras were sent in with the authorized invasion team, and Unohana-taichō was among them. Shouldn't Aizen's surveillance have recorded it in any case?"

Kurotsuchi folded her hands demurely in front of her. "The camera sent with Unohana-taichō was destroyed, and no footage of the battle is available. I am sorry, but if you wish to ascertain what occurred between Unohana-taichō and the Quinta Espada, you will have to make that inquiry of Unohana-taichō. Or perhaps the Sōtaichō, as I believe he would have the details of her report."

Ikkaku scoffed, frustration weighing down his steps until he was stomping back up the stairs.

Yumichika sighed. "Don't mind him, Kurotsuchi-fukutaichō. He's been through a lot recently."

She tilted her head at him, then nodded slowly. "The death of a comrade can be difficult to emotionally process. I have taken no offense at his behavior. However, I ask that you guide him from the premises in such a way as to minimize property damage. Mayuri-sama would not approve of interruptions."

No shit.

"Of course. Thank you for your assistance, Kurotsuchi-fukutaichō." Yumichika knew how to keep professional doors open, even if Ikkaku couldn't be bothered right now. Or ever.

But right now, he had some damage control to do. Grimacing, he hurried up the stairs.

Ikkaku was the only one who could force him to make such ugly expressions.

* * *

And we're back to shortfics! This series of them will likely be quite a bit longer than the last, though, because there's a lot of stuff I need to make happen between the Winter War and the TYBW. I'm open to suggestions on any movies/filler arcs/other stuff between those two things you'd like to see turn into a fic, too, though I'd like to keep the focus on the Gotei 13 and what's up there. (There will also be stuff with the surviving Arrancar.)

I can't promise my pace lately will keep up too long, considering I'm on a break from classes, but I'll do my best to keep stuff coming in a timely manner.

Oh, and here there be shipping. Which will start to happen elsewhere, too. So you're forewarned if that's not your thing. Plot's always my main focus, but realistically, many people are in relationships and those are important to them. So there it is.


	2. Chapter Two: Yang

.

* * *

 _Universal Constant_

A Bleach Fanfic

 _Chaos Theory_ AU

Chapter Two: Yang

* * *

He couldn't fucking believe it.

Something hot hissed under Ikkaku's skin. It was a feeling he had a lot, like if he didn't destroy something, he'd explode. Usually he dealt with it by hitting whoever had managed to piss him off—because it wasn't normal angry or the kind of annoyed he felt about stupid stuff like someone stealing the last of the sake or calling him bald or whatever. That would have been easy to handle with a spar or whatever.

This was… this was…

He didn't fuckin' know. All he knew was he could barely _see_ straight, he was so mad.

"That _fucking asshole_!" He was barely clear of the Twelfth Division before the need to smash something got the better of him. The victim was a tree just outside the wall; his bare fist slammed into it with a satisfying crunch. The breaking sound came from the big crack he'd put in the thing, from a couple feet above the ground up to where the trunk divided into branches. The left half leaned over, birds shrieking and flying away from the sudden damage.

"Feeling better?"

Ikkaku whirled, rounding on Yumichika, who watched him with no expression.

"What the fuck, Yumichika? How are you not angrier than this? You saw what he did. You saw what happened to the captain!" It hadn't been some great battle that did Zaraki-taichō in. Not like he'd wanted. It had been a goddamn coward and a split second of opportunity. What kind of way was that for someone to go? Especially someone like the captain.

It just wasn't… it just wasn't _right_. It wasn't how it was supposed to happen. There was an order to it, and a way it had to happen—and in that order, Ikkaku went first. Defending his captain or Yumichika or his pride or his division or _something_ and having the time of his goddamn life doing it. If Zaraki-taichō _ever_ died, he did it _after_ him.

And Yumichika… he'd just never honestly thought about the possibility of Yumichika dying. He'd probably think it was too damn ugly or something. Even the danger of fighting like they did had never made him figure that Yumichika was gonna die. Risk it, yeah. Get close, sure. But never _actually_ —

"I did see. But what exactly do you think you're going to do about it? Level every tree in the Seireitei?"

Ikkaku was getting a look. He wasn't the sharpest asauchi in the armory, but Yumichika was making it obvious. Arms crossed, eyebrow up, the kind of expression that said _hey Ikkaku, you're being a fucking idiot_. Except he didn't need to say it out loud, and even if he did, he'd probably have bigger words. Ikkaku swore Yumichika was actually brought up somewhere fancy, but they'd never talked much about who they used to be before they met each other.

It didn't matter, so why would they?

He was still mad, but the fuse in his guts had burned out before it exploded. His body felt heavier than it should. Like he'd just used Hōzukimaru's bankai and the extra reiatsu was gone and he was just _tired_. Even guys like him needed to recover between fights. But the last month had felt like one constant fucking fight, only not the fun kind.

"What the fuck am I supposed to do?"

Yumichika always had his shit together. Probably he already knew the answer and was just waiting for Ikkaku to catch up, as usual. It'd sure be helpful if he just _told_ him what to do for once, but he never did that.

So it was surprising when his expression softened and he blew a breath out through his nose. "You're going to go back to the Eleventh and tell everyone you're about to have a match. They're all going to drag themselves out to watch, and then once you've worn yourself out, you're going to sleep. Then, once your head is clear, we're going to talk about this again. How does that sound?"

Even through the fog of tiredness, Ikkaku was interested in this plan. "All right, sure. But who the hell am I fightin'?"

* * *

"Didn't I tell you that the next time we fought, it'd be to the death?" Ikkaku let his hand rest on Hōzukimaru's tsuba, squinting across the practice field at Renji.

Striped little shit didn't look too concerned about it, though, Zabimaru already unsheathed and over one of his shoulders. The other hand rested just above his obi, between the layers of his uniform. He glanced once to the side of the ring, where the officers of the division sat on the porch—the rest of the ring was surrounded by what looked like the entire damn Eleventh. Yumichika shrugged at him, like they were both in on something. As usual, Ikkaku didn't have half a clue what the hell that was all about.

Renji shrugged too. "You said that, not me. And I really don't think you're in any shape to be killin' me right now, so I think I can risk it. Question is: can _you_?"

Ikkaku bristled; a sharp motion yanked his zanpakutō out of the sheath. " _Nobiro, Hōzukimaru_!"

" _Hoero, Zabimaru._ " Renji's reiatsu was a little redder than Ikkaku's, which was more orange. The lights clashed and then faded, leaving both of them armed with their shikai.

A cheer went up from the unseated officers, along with several shouts and jeers. Mostly some version of 'kick his ass,' which was basically normal for a match in the Eleventh. None of that formal quiet bullshit here. Renji was still looking at him like he wasn't even sure what they were doing there, so Ikkaku figured now was a good time to remind him who'd taught who back in the day.

He lunged, the ball of his foot cracking the packed dirt underneath him with the power of the step. Swinging Hōzukimaru in a big arc, Ikkaku clenched his jaw when the blade at the end of the pole clanged hard against Zabimaru, screeching so hard he could feel it echo in his teeth.

" _Sakero_." The pole split into segments, and Ikkaku swung the bottom one for Renji's unprotected side.

It was a move he'd used before, and Renji wasn't fooled, lashing out with his arm and catching it. The slap of the wood pole against the palm of his hand was loud, but his fingers closed over it without flinching. To Ikkaku's surprise, he yanked, the force enough to pull the third seat off his feet. Renji's knee met his nose with a crunch and a sharp burst of pain.

Ikkaku reeled back, blood pouring over his lips and chin, shaking his head. Red drops flew off to either side, landing on the ground. The jeering only got louder, but he couldn't tell what anyone was saying anymore. That background stuff didn't matter anymore.

Renji must have sensed that, because he smirked then, changing his grip on Zabimaru to something more serious. "Found ya," he said, jerking his chin upwards.

Ikkaku grinned, tasting his own blood on his tongue. Cracking his neck to either side, he spun Hōzukimaru's bottom segment, strafing sideways. Renji copied the move, but Zabimaru remained solid.

"When'd you get patient, Abarai?"

"About the same time you got lazy."

Lazy, huh? They'd just have to see about that. Ikkaku lunged again, and this time the fight was on in earnest.

None of the clashes was the complete shitshow the first one had been, but Ikkaku couldn't deny that Renji had gotten a lot better at this. Not just since they'd fought last, either. There was something about him that was more… solid. He didn't lose his cool even when Ikkaku missed his face by an inch with the blade on the end of his zanpakutō. And he never let up on the pressure. Ikkaku's muscles were starting to burn.

 _Use it._

The downward cut Ikkaku was in the middle of went wide.

 _What the fuck?_

Hōzukimaru never talked to him in the middle of a fight. They just didn't work that way.

Renji capitalized on his moment of distraction, Zabimaru curving around and biting into the skin of Ikkaku's thigh. Only his reiatsu let him keep the leg, but it sure as fuck wouldn't be holding his weight for the rest of this match. He managed to get his shit back together in time to hold off the follow-up, jumping away on his good leg and out of Renji's range.

 _Use bankai. Ya won't beat him if ya don't._

Damn spirit was right. Renji was too strong now to take down just with shikai. Ikkaku opened his mouth to call the release—and then shut it again with a click. There were people here. They'd all see.

 _Who gives a shit? Ya heard Yumichika—people know. D' ya want ta win or not?_

He wanted—

Shit. Renji was behind him. Ikkaku knew for a split second before it hit that Zabimaru was about to get him, and braced for the blow. It landed across his back, the teeth of the blade digging into him, past the shihakushō and deep into his muscles. His legs buckled, and Ikkaku went down.

* * *

When he woke up, he knew from experience that he was staring at the ceiling of a room in the Fourth.

Somewhat more surprising was that Renji was still there, bandaged in a couple places but mostly fine as far as Ikkaku could see.

"I ain't dead," he said first. It wasn't really a shock or anything, but Renji hadn't been holding back, either. It was pretty much only that thing that let Ikkaku keep enough of his pride to talk to the guy.

"Nope," Renji agreed, reaching up with a gauze-wrapped arm to scratch his jaw. "How's it feel?"

Ikkaku'd face dropped into a scowl. "Still shitty."

Renji nodded. Probably wasn't a hard answer to guess. "Noticed you didn't use your bankai."

The scowl got deeper. Ikkaku shifted his head slightly; the starched pillowcases were irritating under a shaved head. It didn't look like anyone had been dumb enough to hook him up to any monitors or whatever, though; they'd just mostly closed his wounds and left him there. Didn't mean he had the steam to move yet. "Hōzukimaru told me to."

Renji blinked, dropping his hand back to his knee. "Yeah?"

The obvious question was there even if he didn't really ask it.

"It didn't feel right. If I do that shit and everyone knows… they're all gonna wonder why I ain't captain." Every single goddamn member of the division had been there. Ikkaku wondered if maybe Yumichika hadn't set the situation up that way on purpose. Not to force him one way or the other—that wasn't the kinda thing they did. But to force him to look hard at himself and _admit_ what both of them already knew.

Well, he could admit it. And there was no way he should be captain if this was how it turned out. If he still hesitated like that.

"If it's not what you want, don't do it," Renji said, shrugging, then wincing. Musta pulled at something still sore.

"Yeah, but what the fuck do I do instead?" That was really the meat of the problem. Ikkaku just didn't know what to _do_ with himself anymore. Yumichika asked him if there was anything he wanted to do or anyplace he wanted to go, but there wasn't. He just wanted to do _something_ or go _somewhere_ or what the fuck ever.

Renji stared out the window, heaving a breath out his nose. When he leaned back in the chair, it creaked. His head met the wall, the front legs of the chair coming off the floor at the same time. "I dunno," he said, glancing over at Ikkaku. "That's what you gotta work out. But now you know one thing's off the table for sure. If you wanna know what I'd do… focus on getting your division back together. Find the guys a new captain _somehow_ , and see if it's someone you can follow, or try to beat someday, or whatever. If it's not, cross that bridge when you get there." He snorted. "You're not exactly a planner, Ikkaku—and you don't have to be. Figure it out while you go like you always do."

* * *

Renji left shortly after Yumichika reappeared. Ikkaku still couldn't move much, but he could at least tell that he was getting some control back. Shouldn't be too much longer before he could walk out of here under his own power, which was good because he hated spending time in the Fourth.

Sitting around and thinking wasn't really Ikkaku's speed, but he didn't have a lot of choices on the sitting around part, and Yumichika was pretty quiet right now, drinking tea and doing what looked like paperwork.

Somehow, he managed to feel kind of shitty about that. While him and the rest of the division had spent the last month basically fucking around doing nothing, someone had been doing enough of the forms and other shit to keep the mess stocked and the laundry clean and everyone paid. Well, the Fourth washed the clothes, but keeping everything running took work, too. Work that Yumichika had probably been doing by himself since the captain died.

Not that Zaraki-taichō or Yachiru had ever done paperwork, but other people did, when they were around. The division functioned. Things had a rhythm—and the rhythm wasn't there anymore.

Ikkaku wasn't really sure what to think about any of that.

"You changed your—" With some effort, Ikkaku lifted one arm and gestured to his own face. "Stuff."

Yumichika looked up at that, brush pausing over the page he was working on. Ikkaku knew this look, too. It said _about fucking time you noticed._

"Looks good."

That made him smile, one of those sly ones that only showed up on half his face. Ikkaku liked those ones—they usually meant Yumichika was looking for trouble, or at least happy about something.

"I know." Pause. "Thank you. I'd say you looked good, too, but I don't like to lie to you."

Ikkaku snorted, hard enough that he kinda regretted it a second later when his chest twinged. "Hey. I'm gonna have some fuckin' great scars on my back after this. Don't act like you don't have a thing for those."

Yumichika rolled his eyes, but the smile was still there, which meant he'd done something right. Or said something right, in this case.

"I'll be sure to check, once they actually reach the scar stage. Right now what you have is wounds." He went back to the paperwork for a minute, speedily writing his way through three more forms that Ikkaku honestly probably wouldn't even recognize if he saw them.

"Hey." He cleared his throat, waiting for Yumichika to acknowledge him again before continuing. "I think I wanna stay. At least for now. Even if I'm not captain though—I don't wanna be useless to those guys. Or to you, so—" He fixed his eyes on the stack of papers. "Figure you can give me somethin' to do?"

"You want me to teach you how to fill out forms?" Yumichika looked genuinely surprised, tilting his head and squinting at him. "Are you sure Renji didn't get your head?"

It was Ikkaku's turn for an eyeroll. "Yeah, I'm sure. I ain't sayin' I'm gonna like it, but it ain't right for you to do all that while I sit around and feel sorry for myself."

Yumichika rolled his brush between his fingers, thinking that one over for a moment. One moment stretched into two, and then three, and then Ikkaku wasn't sure what the hell he was even thinking about anymore—it shouldn't be this hard to figure out.

"Uh, Yumichika?"

He held up one finger; Ikkaku closed his mouth.

"Sorry. I'm just taking a minute to appreciate the novelty of imagining you at a desk, doing forms. It's really working for me, by the way."

Ikkaku's mouth flattened into a line. "Really? 'Cause I thought what worked for you was a good fight and some sweat beforehand."

Yumichika raised both brows. "I have depths, Ikkaku. Both of these things work for me. If the connection is really lost on you, I suggest you try it and see what happens."

The suggestion was what did it, cracking Ikkaku's expression until it was a grin. He shook his head, not as bothered by the stiff pillowcase under his head. "Yeah? Might have to, if you put it that way."

Yumichika laughed, and for the first time in a month, Ikkaku felt like shit might not be gone to hell after all.

* * *

He wondered if maybe Unohana took so long to get to his room because she wanted him to squirm.

He wasn't exactly a great patient for her lower seats, and Ikkaku knew it. He _also_ wouldn't put it past her to leave him for a while as a form of revenge for that—he didn't buy whatever gentle-lady front she was putting up. He knew the eyes of a killer when he saw them. Zaraki-taichō had had the same ones. Well, _one_ , most of the time, but Ikkaku figured the point was still the same.

She wasn't near petty enough to heal him any less than perfectly, but making him wait for it? That was definitely something she'd do.

Still, she was here now, and that gave Ikkaku an opportunity he might not have really wanted to go after otherwise. "Taichō?"

Unohana paused for half a second in the act of moving one of his arms to let her access the bandages around his side. "Yes, Madarame-san?"

"That Espada. The one that killed Zaraki-taichō. What happened to him?"

Putting his arm where she wanted it, Unohana nodded to the short shinigami next to her. He had a boyish face, but he was quick with the scissors, and the bandages came away with only a light pull. Her hands turned light green, and she hovered them over his ribcage first.

"He is dead."

The way she said it didn't exactly give the all-clear for more questions, but Ikkaku had to know.

"You killed him?" He grunted when she moved his arm back.

"Turn onto your stomach, please," she commanded. She sounded almost happy about giving the order, like they were talking about nice weather or some shit.

Ikkaku rolled over, gritting his teeth and trying not to ask the question again. No way she hadn't heard him the first time.

"And what if I did?" Unohana asked after a minute. "Would I be expecting a challenge from you at some point for the captaincy of the Eleventh?" He couldn't read her tone then, not even when he craned his neck to look back at her over his shoulder. There was just something about her—he couldn't stand not being able to see her when she was in the same room. Like he really didn't want to give her his back, even though he didn't have a choice.

"No. Just—tryna figure out where to go from here. Wanna do it the right way." For Zaraki-taichō and the Eleventh. Making it up as he went along, like Renji said.

Unohana hummed. Thoughtfully, he figured, like she was considering something he'd said. "As I recall, the rule is that Kenpachi is the title belonging to whomever can best the former Kenpachi in battle," she pointed out. "The mere act of killing someone is not the same thing, as Zaraki-taichō's case amply demonstrates."

"Best in battle…" Yumichika seemed to see something in the words, at least. He'd stood when Unohana entered. Now he was leaning against the wall, arms crossed. "We… saw that happen, didn't we, Ikkaku?"

His face pulled to the side; he'd pushed himself halfway up before Unohana forced him back down with a firm hand. That made him settle for shooting Yumichika his best disbelieving look. "An Espada? You can't be serious."

Yumichika shrugged. "Can't I? The Eleventh only cares about strength, right? The rule is that the strongest person is in charge of it, and the way that leadership passes from one Kenpachi to the next is in a fight. A fair fight, like the one with Grimmjow."

Ikkaku opened his mouth to argue with that, except he couldn't really think of anything to say. What both of them said was true. Hell, it wasn't like _he_ gave a shit about the rules. If there even were any. 'Hollows can't be shinigami' was probably one of those things that was so fucking obvious no one had actually ever made it into a rule.

"The ranks have handled a Quincy," Unohana added, like it wasn't any kind of big deal. "Perhaps they could stretch a little further still. I'm sure you'd have to discuss it with the Sōtaichō, however."

It was a hell of a fucking idea… but it was an idea. And now that it was in Ikkaku's head, he couldn't get rid of it. When did the Eleventh ever do anything like anyone else anyway? Their division was the one with people who couldn't do fucking kidō half the time, people who would have been scum on the streets of Rukongai if they didn't have the fight instinct down in their bones. The kind of people no noble or respectable types would even give the time of day to. And they made something of all that. Made their own way, without giving a damn what everyone else thought. Zaraki-taichō had never taken a _shunpō_ step in his fuckin' life.

And Ikkaku knew. He knew the captain would want this done the Eleventh Division way. Their way.

 _Fuck it._

"Guess we'll be talkin' to him next, then."

* * *

Ikkaku had always thought that Kyōraku was a pretty decent guy. He definitely didn't have the demeanor of most of his friends, but he knew how to have a good time, and wasn't up on some high horse like Kuchiki was, even though they were both nobles.

Even right now, he couldn't really complain about the situation. The new Sōtaichō had welcomed them into his office, where he'd immediately broken out the sake and told them to sit. Now, a couple bottles in, they were finally coming around to the actual discussion. It was probably a good sign that he hadn't laughed them out of the place already. In fact, he looked like he was actually thinking about what they'd said, which was… kinda surprising, honestly.

"I've seen the recordings," he admitted, tipping his dish back and sighing after he swallowed. He leaned back against the desk behind him, wincing when it scraped against the floor under his weight. "I think there's probably an argument to be made that you're right. Technically. I just don't know if it's feasible in… well, any other way, really."

Ikkaku blinked, his eyes blurring for a second. A couple more cleared them, though, and he focused on the Sōtaichō's face. He had the eyes, too. The ones you only got after seein' too much shit. Hell, he was so fucking old most of the buildings in the Seireitei were probably younger than him.

"What's the problem, exactly?" he asked, leaning sideways and bracing himself on one hand.

Yumichika muttered something that sounded like _Central 46_ into his cup.

Kyōraku nodded. "Among other things. There's also the really obvious question: would Grimmjow even be interested in something like this? Would the rest of the division accept it? Much less the rest of the Gotei 13. I'm not one to cling to tradition any more tightly than absolutely necessary, but this would be unconventional even for me."

"How much more unconventional would it be than letting Zaraki-taichō join, though?" Yumichika asked, pouring himself another cup. "We both know that wasn't exactly superb tactical decisionmaking. He didn't have any of the normal shinigami skills, and no one ever taught him any. It's pretty obvious that he was being kept around because someone thought he was dangerous enough to watch from up close."

Kyōraku raised both eyebrows. "That's an interesting hypothesis, Yumichika-san. It even has the benefit of being true. But whatever else he might have been, Kenpachi-san wasn't part Hollow." He looked thoughtful, though, like he didn't quite believe what he was telling them. Or believed the obvious part, but didn't really think that it counted against what Yumichika said.

Ikkaku wasn't sure what else he could possibly say. He'd made the best case he could, and while it'd piss him off if Central 46 or some other dumb fuckers who thought they knew how to run an army from far away stopped it… there wasn't a whole damn lot he could do about that.

"He knew that girl, right? Kurosaki? Maybe she knows something that could help."

The Sōtaichō hummed. Ikkaku knew not committing when he heard it, but what he didn't know was the reason. He shot a look at Yumichika, but he was keeping quiet about this part. Probably a good hint that shutting up about that was the way to go.

"I'll think about it. There's a lot of captains to replace, after all. It might be that putting the situation the right way could convince the Central 46 that desperate measures are necessary. But none of this will happen overnight, if it happens at all. Your division's probably going to need the two of you in the meantime." He said it like he was talking to both of them—but he looked at Ikkaku.

"Yeah," he replied. "I get that now."

"I'm glad to hear that, Ikkaku-san."

* * *

When that Quincy kid and the ryoka attacked, they'd at least done some damage to the place between them. Something that made it easy to tell that something had happened. Important stuff.

Now, though, the buildings were all the same. The most damage that had happened to the Seireitei because of the whole war had been Ikkaku punching a tree because he was pissed about something that happened in it. He knew that was supposed to be a good thing. The point was to defend the place after all, even if he'd never really gone in for the whole 'protect the balance' thing. It just hadn't mattered, been some way-over-his-head thing that fancy people talked about and sent people like Ikkaku to fight and maybe die for.

But he sorta wanted there to be some damage. What did the fancy people care about what had happened, since it didn't even touch their stuff? Their lives? They fuckin' should care, but he just couldn't imagine it.

"Hey Yumichika."

"Yes, Ikkaku?" His—they never really did come to any kinda agreement about what they were called. His _friend_ wasn't enough. His _lover_ implied schmoopy shit that neither of them wanted or cared about. Yumichika was the other half of Ikkaku, if that didn't sound really damn weird to say since they were both whole people. He was just Yumichika and also Ikkaku's _something_ , but fuck if anyone else's words were good enough to say what.

But now he was looking at him with one eyebrow above the other, half a smile on his face like he knew what Ikkaku was thinking about before Ikkaku did.

That was probably true, honestly.

"Do you think… it was weak of me? Not to wanna be the captain?" To have spent a month not knowing _what_ he wanted?

Yumichika huffed, then shook his head. "No. The weak thing would have been insisting on taking up a burden you weren't prepared to carry. If you weren't ready and had done it anyway, you would have made the division suffer. But you didn't." He shrugged. "You know me: as long as you don't regret it, then I think it's the right thing. I think you would have regretted being captain right now."

"Just right now?"

"Yes."

He said it with such confidence that Ikkaku believed it. Reaching the entrance to the Eleventh first, Yumichika slid the barracks door open and stepped inside, leaving Ikkaku to close it behind him. The troops were all out training at this time of day, or doing paperwork when the place was functioning right.

Ikkaku wasn't quite prepared for his back to hit the wall; the just-healed wounds there twinged, shooting sparks across his skin. Yumichika's hand closed over his throat—not hard enough to choke him, just enough to make the threat of it real. Ikkaku hissed, breath coming out through clenched teeth.

Yumichika swallowed the sound, leaning up to press their lips together, demanding and abrupt. Ikkaku's hands found his waist, fisting in the loose cloth of his uniform, and he pushed back, forcing both of them several steps down the hall before he turned left, and it was Yumichika that hit the wall. The hand on his neck squeezed slightly, Yumichika's teeth digging into his lower lip.

Ikkaku grunted; Yumichika broke the kiss long enough to smirk up at him. "Welcome back, Ikkaku. I've been waiting."

"My bad," he replied, jamming his fingers into the gap between the doorjamb next to Yumichika's shoulder and the door. With a shove, he pushed it open far enough to fit them both inside, only barely remembering to shut it again behind them.

Some things, he figured, never changed.

* * *

 _Term Dictionary:_

 _Hōzukimaru_ \- 鬼灯丸 – "Demon Light." Ikkaku's zanpakutō. Initially appears to be a spear, but upon the command _sakero_ (裂けろ; "to split"), it becomes a three-section staff. The release command is _nobiro_ (延びろ), the imperative of "to grow."

* * *

So… I don't write ships very often. And I found these two pretty challenging because their personalities are kind of one-note in canon, so I had to add some depth before I could really extrapolate what their relationship was like. If I took a bad turn along the way somewhere, please feel free to let me know. Learning to write new stuff is always an adventure. I have way more experience with fight scenes than people in relationships, heh.

Also, Happy New Year, y'all. May yours be filled with only awesome things.


End file.
